When do liquidated damages add up to an unenforceable penalty?

Focuses on the case of Alfred McAlpine vs Tilebox which gives helpful guidance about how the court in England tests whether a high level of liquidated damages stipulated in a contract make a particular provision a penalty and therefore unenforceable. Ruling of the court that for a pre-estimated sum in damages to be enforceable, it has to be reasonable; Potential losses of Tilebox; Enumeration of the grounds to consider that a liquidated damages clause not a penalty.